FIG. 1 diagrammatically illustrates a conventional example of a PLMN coupled to a mobile station (MS) 13 via a physical radio interface 17. The PLMN includes a radio access network 11 coupled to a core network 15. The core network 15 can be either a packet switched core network or a circuit switched core network. The mobile station 13 (any type of mobile radio transceiver) communicates with a base transceiver station (BTS) of the radio access network 11 via the radio interface 17. The physical layer, also referred to as layer one or the PHY layer, of the mobile station 13 (and the physical layer of the corresponding BTS of the radio access network 11) is responsible for transmission of data over the radio interface 17. On the transmitter side, layer one (L1) performs tasks including channel coding (error detecting and error correcting), interleaving, burst formatting, modulation and radio transmission. On the receiver side, layer one performs tasks including radio reception, synchronization, channel estimation, demodulation (equalization), de-interleaving and channel decoding (error correction and error detection).
Examples of the core network 15 include circuit switched or packet switched GSM, and circuit switched or packet switched UMTS. The radio access network 11 can be, for example, the GSM/EDGE radio access network (GERAN).
The PLMN of FIG. 1 is capable of providing a variety of services to its end users, each service having its own specific requirements regarding error rates, delay, etc. In order to accommodate the required services, the core network 15 requests from the radio access network 11 bearer services that transport information between the mobile station 13 and the edge of the core network 15. If the core network is a third generation (3G) core network, for example a UMTS network, the bearers (which provide the bearer services) are referred to as radio access bearers or RABs. A request for an RAB from a 3G core network to the radio access network 11 is specified by a set of RAB parameters. The RAB parameters contain a description of the information to be transferred, together with requirements on bit error rates, block error rates, delay, etc.
The RAB request contains information about the service to be supported by the call that is being set up, for example maximum bit rate, guaranteed bit rate, maximum payload size, maximum error rate, etc. The information in such an RAB request is typically independent of the type of radio access network 11. For example, the RAB request looks the same whether the radio access network 11 is GERAN or UTRAN.
In conventional radio access networks such as GERAN or UTRAN, layer one of the radio interface provides transport channels which either transport information from higher layers to the actual physical radio channel(s), or which transport information received from the actual physical radio channel(s) to the higher layers. Conventionally, these layer one (L1) transport channels are divided into two main types, optimized and generic.
With the optimized approach, the layer one transport channels are set up based on exact knowledge of the transported information blocks for a particular service. This permits, for example, voice to be transported efficiently over the radio interface. The speech frames can be unequally protected (UEP) and, just as important, unequal error detection (UED) can be used.
In the generic approach, the layer one transport channels are set up without detailed knowledge of the service. Generic transport channels use equal error protection and detection. Padding and segmentation can be used to handle variations in the payload size.
The optimized approach provides good spectrum efficiency for speech, for example AMR (adaptive multi-rate), but the optimized channel approach disadvantageously requires specific channels to be defined for each service. On the other hand, although generic transport channels are more flexible, they disadvantageously lead to poor radio interface performance for certain services, for example speech services.
Conventional layer one transport channels are static in the following aspects: the number of information bits to transfer per radio block is fixed; the error detection scheme for each part of the information block is fixed; the error correction scheme (including code type and rate) for each part of the information block is fixed; the puncturing pattern is fixed; and the interleaving is fixed.
There are a number of conventional predefined layer one transport channel schemes, for example optimized schemes that have been developed for AMR, and generic schemes such as GPRS, EGPRS and ECSD. According to conventional operation, higher layers choose a set of these predefined schemes depending on the service that is being supported.
As indicated above, the layer one transport channels generally interface between higher layers and the physical radio channel(s). For example, GERAN provides for radio transport via physical subchannels, where each physical subchannel is a sequence of GSM time slots that are allocated for the particular data transfer. A physical subchannel can be either a full-rate (FR) channel or a half-rate (HR) channel. A set of consecutive GSM time slots on a physical subchannel, used for the transfer of one block of data received from (or bound for) one or more layer one transport channels, is called a radio block. In some conventional systems, for example those that utilize GPRS and EGPRS, a radio block consists of four GSM time slots.
One or more types of modulation can be available for use on a given physical radio channel. For example, one or both of GMSK modulation and 8-PSK modulation can be used on the aforementioned GERAN physical subchannels.
It can therefore be seen that the actual gross data rate available for a data transfer depends on the data rate associated with the physical radio channel and the modulation used on the physical radio channel. In the GERAN example, the data rate available for data transfer depends on whether the physical subchannel is full-rate or half-rate, and also depends on whether the modulation is GMSK, 8-PSK, or a combination thereof.
Some examples of conventional layer one transport channel schemes for services defined in GERAN are described below.
The layer one transport channel schemes for AMR are examples of optimized schemes, i.e., they are tailor made to give the best possible performance for a particular speech codec. To provide transport of AMR speech over the radio interface, a number of layer one transport channel schemes are defined. There are currently eight different speech codec modes defined for AMR. For each of these eight modes, a layer one transport channel scheme for transport over a full-rate physical subchannel with GMSK modulation is defined. Further, for six of the modes, layer one transport channel schemes are defined for transport with GMSK on a half-rate physical subchannel.
The speech information is delivered to layer one in blocks (also denoted as speech frames) the size of which depends on the AMR mode. One speech frame is delivered every 20 ms. Below follows a description of exemplary layer one transport channel processing for the AMR 12.2 mode for transport over a GMSK FR channel.
The speech frame delivered from the speech codec consists of 244 speech bits and two inband bits (used for signalling). Of the speech bits, 81 are more important for the speech quality, and therefore more sensitive to errors (called class 1A bits). The remaining 163 bits are less sensitive (called class 1B bits). The speech bits are sorted by layer one according to their importance, putting the class 1A bits first and the class 1B bits after. Six CRC bits are added after the 81 class 1A bits, giving 87 bits. The class 1B bits are put after the CRC bits. All these bits are then encoded together using a convolutional coder with rate R=½. This results in an encoded block of 508 bits. Sixty encoded bits in the latter part of the encoded block (corresponding to the class 1B bits) are punctured (i.e., not transmitted). Effectively, this increases the code rate of the class 1B bits, giving them less protection. This results in a block of 448 bits. The 2 inband bits are encoded to 8 bits using a block code. The encoded inband bits are put together with the encoded speech bits, giving a block of 456 bits. Finally, the 456 bits are diagonally interleaved over 8 half bursts and transmitted over the radio interface.
For each of the other AMR modes, similar layer one transport channel schemes are defined. A particularity of the layer one transport channel schemes for AMR is that different parts of the information are given different degrees of protection against errors. Further, one part is protected with error detecting codes, while other parts are not. This unequal treatment of different parts is referred to as unequal error protection (UEP). The layer one transport channel scheme for each mode is very specific for that mode, and can not be used for any other mode, and definitely not for other services.
The layer one transport channel schemes of EGPRS are examples of generic schemes. They are not optimized for a particular service. The packets of data to be transferred can have any size. The packet is segmented by the RLC/MAC layer into RLC data blocks of a size that fits the layer one transport channel schemes. On the receiving side, the packet is reassembled from the received RLC data blocks.
The layer one transport channel schemes of EGPRS do not treat any particular part of the RLC data block differently. However, the RLC/MAC layer adds an RLC/MAC header to each RLC data block, which is given more protection than the RLC data block. In some sense, the EGPRS layer one transport schemes are optimized, since they require a specific RLC/MAC header size and a specific RLC data block size. However, they are not optimized for a certain type of user data (i.e., they do not assume any particular size or structure of the data packet before segmentation).
In EGPRS, nine different layer one transport channel schemes are defined, called MCS-1 to MCS-9 (Modulation and Coding Scheme). Each has a different RLC data block size. MCS-1 to MCS-4 uses GMSK modulation, while MCS-5 to MCS-9 uses 8-PSK modulation. In GERAN, only FR physical subchannels can be used. The nine schemes have different degrees of error protection. In each radio block the scheme is chosen based on the channel quality, to maximize the throughput.
Below follows a description of an MCS-6 example.
To layer one a block having a total of 622 bits is delivered. The first 28 bits are the RLC/MAC header, of which the first three bits define a field called USF. The remaining 594 bits are the RLC data block. The USF field is encoded with a block code to 36 bits. To the 25 remaining RLC/MAC header bits, an eight bit CRC is added, giving 33 bits. These are then encoded with a tail-biting convolutional code with rate R=⅓. Finally, one spare bit is added, giving a block of 100 bits. The encoded RLC/MAC header is interleaved. To the 594 bits of the RLC data block a 12-bit CRC is added, giving 612 bits. These are encoded with a convolutional code with rate ⅓, and punctured. The puncturing is evenly distributed throughout the block, giving equal protection to all bits. After puncturing, the block has 1248 bits. The encoded RLC data block is also interleaved. Finally, the encoded USF, RLC/MAC header and RLC data block are put in a radio block and transmitted.
New services are continuously being introduced in the PLMN, and radio access networks such as GERAN are expected to provide bearers capable of handling these services. For example, the following new services have been discussed in the GERAN standardization: adaptive multi-rate wideband speech (AMR WB); and voice over IP services.
Further, it is desirable to be able to transport the information of such new services over different types of physical channels (e.g. FR and HR) and with different modulations (e.g. GMSK and 8-PSK) Another desirable improvement is to be able to transport old services over new physical channels or with new modulations. For example, AMR narrowband (NB) with 8-PSK over a half-rate physical subchannel has been discussed. For each combination of service, physical channel and modulation, new layer one transport channel schemes are needed.
Some drawbacks associated with the current way of specifying layer one transport channels in GERAN are discussed below:
New circuit switched voice services have been introduced in GERAN. The Narrowband AMR is being designed for HR 8-PSK channels. The new speech codec wideband AMR is also being introduced, both for FR GMSK and FR 8-PSK. These new codecs require at least 8 rates per physical subchannel (FR, HR, etc). Each rate needs to have its own convolutional coding and puncturing table in memory. At the same time, each channel coding rate has to have performance requirements for 22 different propagation conditions specified in 45.005. After implementation of the new channel coding in the product, everything needs to be tested and verified.
For voice over IP, when adding an IP header to the voice frames, it is no longer possible to use the existing optimized voice bearers defined for GSM since the payload format changes. If IP header compression is used, the size of the compressed header will vary over time. A new layer one transport channel scheme is needed for each speech codec mode/IP header size combination to transport the IP header together with the speech. Therefore “Optimized VoIP” has been discussed in GERAN standardization, where the basic idea is to remove the IP header. By doing so, it is possible to use standard AMR optimized channel coding. Some disadvantages with the current solution are absence of IP transparency, handover between cells with different AMR capability, and a different solution compared to UTRAN (the VoIP application will be RAN dependent).
The IP Multimedia Subsystem is being defined in 3GPP for REL-5. One example is unequal error protection on packet switched conversational multimedia services where several subflows (bit classes) will be transported down to the physical layer. This enables robust header compression (ROHC) to be used in combination with UEP/UED. Currently, GERAN can not use the same solutions developed for UTRAN.
Additional services can be expected in the future, for instance new streaming services for video applications. Also for these, new layer one transport channel schemes are needed.
Thus, the traditional way of using predefined and fixed layer one transport channel schemes disadvantageously implies memory-consuming and complex implementations at the physical layer, as well as costly changes in order to be able to provide new services. New layer one transport channel schemes are needed for each new service and for each new physical channel on which a service must be transported.
The invention advantageously provides flexibly configurable layer one transport channels for producing radio blocks in response to communication information and for extracting communication information from radio blocks. According to some exemplary embodiments, each transport channel includes an encoder or a decoder coupled to and cooperable with a data puncturer or a data repeater. According to some exemplary embodiments, an information source produces for each transport channel first configuration information and second configuration information, wherein the first configuration information is indicative of how the associated transport channel is to be configured if a first modulation type is used for a current radio block, and wherein the second configuration information is indicative of how the associated transport channel is to be configured if a second modulation type is used for the current radio block. According to some exemplary embodiments, the physical layer includes a description information source that provides description information from which various configurations of the transport channels can be determined. The description information source provides the description information in the physical layer in response to further information which the description information source receives from a higher layer and which is indicative of a service request initiated by a communication network. According to some exemplary embodiments, one of the transport channels is enabled to extract its associated communication information from a radio block while another of the transport channels is maintained disabled. The one transport channel provides the extracted communication information to a decision maker in a higher layer. In response to the extracted communication information, the decision maker decides whether the other transport channel should be enabled, and provides to the physical layer an indication of its decision. The other transport channel can then be enabled if the decision maker provides an enable indication.